In the prior art, a linerless label adapted to save resources has been employed as a band-shaped continuous label sheet. The linerless label does not have a liner sheet (release sheet) on which an adhesive layer on a back surface of a label substrate is temporarily attached.
A thermal printer 1 for such a linerless label has a feeder unit 3 of a linerless label 2, a detection unit 4, and a print unit 5 as illustrated in FIG. 10.
The linerless label 2 is wound in a roll shape and is loaded on the feeder unit 3. As illustrated in the partially enlarged view of FIG. 10, the linerless label 2 has a band-shaped label substrate 7, an adhesive layer 8 formed on a back surface of the label substrate 7, an underlying heat-sensitive color developing layer 9 formed on a front surface of the label substrate 7, and an overlying release layer 10.
In this manner, since the release layer 10 is formed on top of the linerless label 2, the adhesive layer 8 comes into contact with the release layer 10 by winding the linerless label 2 in a roll shape. Therefore, even when a roll of the linerless label 2 is loaded on the feeder unit 3, it is possible to continuously feed the linerless label 2 without sticking between inner and outer layers.
The linerless label 2 continuously discharged from the feeder unit 3 is fed to the print unit 5 from the feeder unit 3. The detection unit 4 and a guide roller 11 that guides the linerless label 2 are provided in the middle of a feeding path of the linerless label 2 from the feeder unit 3 to the print unit 5.
The detection unit 4 has a mark sensor 12 such as a transparent optical sensor to detect a relative position of the linerless label 2 with respect to the print unit 5 by sensing a position detection mark (not shown) printed on the linerless label 2 in advance at a predetermined pitch.
The print unit 5 has a thermal head 13 and a platen roller 14. The linerless label 2 continuously discharged from the feeder unit 3 is fed to a gap between the thermal head 13 and the platen roller 14.
In the print unit 5, the linerless label 2 is nipped and fed by rotating the platen roller 14, and printing of predetermined contents is performed on a surface of the label substrate 7 by supplying data to a heating element 15 of the thermal head 13 and developing a heat-sensitive color developing layer 9 formed on the surface of the label substrate 7.
The linerless label 2 is cut out along a line of perforations (not shown) formed on the linerless label 2 at a predetermined pitch and is issued as a single tag of the linerless label 2A. Alternatively, the printed linerless label 2 may be cut out at a predetermined pitch using a cutter such as a movable blade or a fixed blade to issue a single tag of the linerless label 2A.
In the thermal printer 1 having such a configuration, a releasable material such as silicone rubber is used on the platen roller 14 coming into contact with the adhesive layer 8 of the back surface of the linerless label 2 to guarantee non-adhesiveness. In addition, a downstream-side wraparound prevention member 16 having non-adhesiveness similar to that of the platen roller 14 is provided in a downstream side of the feeding direction from the platen roller 14.
It is desirable to design a gap between the downstream-side wraparound prevention member 16 and the platen roller 14 as small as possible. Meanwhile, if the platen roller 14 is detachably installed considering maintainability, and the gap between the downstream-side wraparound prevention member 16 and the platen roller 14 is excessively small, the downstream-side wraparound prevention member 16 may interfere in installation or removal of the platen roller 14.
In this regard, a technique has been proposed, in which the downstream-side wraparound prevention member 16 is assembled with a platen bearing that rotatably supports the roller shaft 140 of the platen roller 14, and the platen bearing is detachably installed in the support member provided in a device housing as a fixing portion, so that the platen roller 14 and the downstream-side wraparound prevention member 16 are unitized into a single assembly, and the single assembly is detachably installed in the device housing (see JP 09-314948 A).
In the technique of JP 09-314948 A, a pair of notches are formed on an outer circumference of the platen bearing, and the downstream-side wraparound prevention member 16 is assembled with a pair of notches. In addition, the platen bearing is inserted into a concave portion of the support member and is fixed by rotating a pair of notches of the platen bearing in synchronization with the downstream-side wraparound prevention member 16.